In the past, floating dry docks have been created by the assembly of a number of identical floating subunits. These units have been roughly cubical with tabs projecting from the vertical edges at or near the horizontal midline. By fastening the adjacent tabs to each other, floating docks with substantially flat deck surfaces of many different configurations have been assembled.
Examples of such units and docks assembled from such units are found in U.S. Pat. Nos. 3,824,644 and 4,604,962. These patents describe hollow, roughly cubical floatation units which in practice have been manufactured about 16 to 20 inches on a side. The units have been molded from a suitable plastic material with tabs which project from each vertical edge positioned so that a dock of virtually any shape with a substantially flat deck or top surface could be formed. With a personal watercraft, such as a jet ski, or with other small craft, such as a motorboat or jet boat under about 18 feet in length, the goal of the floating dry dock has been to make it possible to drive the craft up onto the dock. This would enable the operator to get on and off the craft without getting in the water and would also permit the craft to be stored out of the water.
Attempts to accomplish these goals using the prior art floatation units described above have not been entirely successful. The dry docks assembled from such prior art units have been either too high above the water to permit a personal watercraft to be driven on, or too low to keep the driver and craft out of the water entirely. Keeping the craft high and dry when not in use is important to protect the machinery of the craft.
The above problem was addressed in U.S. Pat. No. 5,529,013 which describes a floating drive-on dry dock for personal watercraft or small craft. FIG. 1 shows a prior art dock constructed in accordance with the teachings of this patent. The dock 10 was assembled from a combination of tall and short hollow, air-tight floatation units. The tall units 12a-l are roughly cubical and have tabs projecting from about midway along their vertical edges. The short units 14a-f have tabs positioned to make an upper deck surface continuous with the deck surface formed by the tall units. The short units are able to flex downward when a craft is driven onto the dock, but resist flex in the opposite direction when the craft is in place and so form a stable surface that can be walked on.
The docks illustrated in FIG. 1 have been made wider in an effort to hold large, heavy watercraft. Such docks often experience a substantial bowing or flexion about the longitudinal centerline (keel) of the craft, thereby causing a substantial amount of stress on the tabs which connect the various subunits together and causing the craft to contact the water. An example of this problem is illustrated in FIG. 2, which is an end view of a dock similar to that shown in FIG. 1 but modified to be five cubes wide.
The tall units 12a-l (FIG. 1) are substantially all identical to each other, and in the subsequent description the reference numeral 12 without a suffixed letter is used to designate a tall unit generically, while the specific suffixes are used to refer to particular tall units. A similar nomenclature is used in connection with the short units 14a-f.
The tall units 12 are generally cubical, although the vertical edges 16 are beveled as shown in FIG. 1. A tab 18 projects from each beveled edge 16. The tabs are vertically staggered to facilitate connecting each floatation unit 12 to its neighbor, as illustrated schematically in FIG. 1. By staggering the distance down from the deck surface 20 of the tabs 18, it is possible to connect the tall floatation units with their top surfaces approximately coplanar so as to make a deck surface 20 for the dock 10 that is more or less flat and without abrupt steps.
The short floatation units 14 are similar to the tall units 12 except in the distance from the tabs to the bottom wall. The short units 12 have tabs 18 that are vertically positioned along the beveled corners 16 the same distance down from the deck surface 20 as are the corresponding tabs 18 of the tall units 12.
As a consequence of this arrangement, the short units 14 can be interconnected with the tall units 12, and the deck surface 20 produced will be generally planar and substantially without abrupt steps.
The floatation units 12 and 14 may consist of high density polyethylene (HDPE). This material has proven to be extremely rugged and to resist corrosion as well as the degradation resulting from attachment of marine flora and fauna. Moreover units which use HDPE exhibit an appropriate balance between flexibility and thickness. The tabs 18 are slightly more than 1/2 inch thick. Each of these tabs has a central opening 24 through which a fastener may be placed. Fasteners and openings like those shown in U.S. Pat. No. 3,824,644 have proved suitable for connecting floatation units 12 and 14 to each other where there are four tabs to be joined. Where three or fewer tabs are to be joined, a plastic nut and bolt assembly (not shown) has been used.
The prior art dock 10 of FIG. 1 is constructed so that surfaces on which a modest-size watercraft slides are submerged only while the watercraft is being ridden onto the dock 10, but which remain above the surface before and after the craft is driven onto the dock 10. The result is a dock that does not accumulate barnacles or other harmful marine growth on the surfaces which contact the craft. However, when the dock 10 of prior art FIG. 1 is expanded for use with a larger size watercraft, undesirable bowing and flexion is exhibited as illustrated in FIG. 2.
FIG. 2 is a view of a five cube wide prior art dock 21 looking endwise from the bow toward the stern. FIG. 2 illustrates a bowing or flexion caused by forces exerted on the deck surface 20 of the dock 21 in the direction F. The weight of a larger craft upon the deck surface 20 may cause the watercraft on the deck surface 20 to make contact with the water while stored on the dock 21. As discussed earlier, this disadvantageously causes the water to contact the bottom of the boat resulting in barnacles or other type degradation of the boat hull. Moreover with craft weighing in excess of 500 lbs, the cubes themselves may be distorted, resulting in even more bowing. Such a bowed dock may also be hard to walk on because of its slope.
As noted above, it is desirable for the craft to be entirely out of the water while docked. This enables the operators to enter their boat without getting in the water, and also enables the craft to be stored out of the water entirely. Keeping the boat out of the water entirely while stored on the dock is important to protect the machinery of the craft as well as to prevent marine growths, such as barnacles, from scratching the bottom surface of the craft each time the craft slides onto or off of the dock.